Seagrass influence on mitigating ocean acidification and warming impacts on tropical calcifying macroalgae

Area of Science:

• Marine Biology
• Oceanography
• Ecology

Background:

• Ocean acidification (OA) and warming threaten marine calcifiers by reducing calcium carbonate availability.
• Seagrasses are known carbon sinks, prompting investigation into their potential role in mitigating climate change impacts on marine life.

Purpose of the Study:

• To determine if seagrasses can mitigate the adverse effects of ocean acidification and elevated temperatures on three species of calcifying macroalgae.
• To assess the individual and combined impacts of OA and thermal stress on Mastophora rosea, Halimeda opuntia, and Mesophyllum sp.

Main Methods:

• A 12-week mesocosm experiment cultured three calcifying macroalgae species with and without seagrass.
• Gradually increasing stress conditions were applied: ambient, OA alone, OA with moderate warming (28°C), and OA with high warming (31°C).

Main Results:

• Ocean acidification and warming negatively impacted Mastophora rosea.
• Halimeda opuntia showed greater sensitivity to elevated temperatures than to OA.
• Mesophyllum sp. demonstrated resilience to both OA and warming conditions.
• The presence of seagrass did not significantly mitigate the negative effects of OA and warming on any of the studied macroalgae.

Conclusions:

• Seagrasses do not appear to offer protection to these specific calcifying macroalgae against combined ocean acidification and warming.
• Different calcifying algae species exhibit varying sensitivities to environmental stressors, highlighting the complexity of predicting ecosystem responses.